During the using of common manual tools such as screwdrivers and torque wrenches, there is a movement limitation of the human hand in rotation direction, namely the inability of the human hand to turn continuously in one direction. The operation of such a tool whose rotation axis of the handle is coaxial with the tool's main shaft consists of a repetition of the following cycle: first, the hand rotates the handle in the desirable direction (e.g., tightening or loosening a screw); second, the hand rotates in the opposite direction to reposition the tool for next cycle. During the second portion of the above mentioned cycle, the band's reversed rotation can be achieved by re-grasping the handle after releasing it, or by the tool which is equipped with a one-way means such as a ratchet to keep the main shaft stationary during the reversed rotation of the handle, or by re-inserting the tool bit to the screw after extracting the bit from engagement with the screw. However, in any case, the hand's reversed rotation could not bring any effective advance of the fastener, and therefore it becomes a wasted movement. U.S. Pat. No. 5,931,062 discloses a mechanical rectifier, which comprises a shaft; two driving elements mounted on the shaft, each having a one-way clutch interposed between it and the shaft, with the clutches oriented in the same way on the shaft so that the shaft is always entrained in only one direction of rotation when either one of the two driving elements is rotated in that direction, and the shaft is overrun by a driving element that is rotated in the opposite direction; a rotation means positioned along the axis of the shaft and engaging a selected one of the driving elements; and a reversing mechanism coupling the two driving elements together and forcing them to always rotate in opposite directions so that one driving element entrains the shaft and the other driving element overruns the shaft, thus causing the shalt to always turn in only one direction, regardless of the direction of rotation of the driving elements, so that transfers the bidirectional rotations of the rotation means (e.g., a handle) into the unidirectional rotation of the shaft. This mechanical rectifier can efficiently utilizes the rotations of the rotation means in either way, i.e., no matter the handle rotates clockwise or counterclockwise, the shat rotates in a same direction, therefore it can improve the efficiency of hand motion, and save operation time.
However, the converting mechanism of that invention can only make the shaft rotate in one direction. To meet the requirement of rotating the shaft in two ways (e.g., tightening or loosening a fastener in the application of a screwdriver), the handle of that invention must be able to be removed from the shaft which is coaxial with it, and the two ends of the shaft (assumed to be end A and end B) should be able to adapt with tool bits. Assuming end A is used to tighten a fastener in the beginning, in order to loose this fastener, the handle mounted on end B of the shaft must be removed from the shaft, then people should re-mount the handle to end A of the shat, insert a suitable tool bit on end B, and then start the fastener-loosing action. If the fastener to be loosed is the same type as the one being tightened in the beginning, the tool bit must be removed from end A before the handle re-mounting, and be inserted to end B. It is obvious that the direction-switching of the shat is very inconvenient. It is even troublesome to replace the bit to the two ends of the shaft for multi-purpose screwdrivers with replaceable bits. Furthermore, it means the integrity of the whole screwdriver itself can not be ensured and its parts are easy to get lost, to assure the handle can be removed from the shaft easily.
Therefore, it is desired to develop a bidirectional mechanical converting unit which can switch the rotation direction of the shaft conveniently.